Yeah, the ring is a steel hose clamp, like Lucius said. They can be had for $1.50. Get one that's a bit bigger than you think you need and cut off the slack.

Also, I put a rubber band around my focus ring before I put the clamp on it (to protect it). You can also put another rubber band on the ring, draw your witness marks for focus, and wedge a paper clip in the focus pull ring to show you where your focus is. It's all very neat.

Loving it, @fleetinglight. Shooting a ton with it, although the follow-focus is off for the time being. A little cumbersome to leave it on for just stills. But it only takes a few seconds to put it on and take it off, so you're golden.